1. Technical Field
This disclosure relates to a window unit, a window device, a laser apparatus, and a system for generating extreme ultraviolet (EUV) light.
2. Related Art
In recent years, as semiconductor processes become finer, photolithography has been making rapid progress toward finer fabrication. In the next generation, microfabrication at 60 nm to 45 nm, and further, microfabrication at 32 nm and beyond will be required. Accordingly, in order to meet the demand for microfabrication at 32 nm and beyond, for example, an exposure apparatus is expected to be developed, in which a system for generating EUV light at a wavelength of approximately 13 nm is combined with a reduced projection reflective optical system.
Three kinds of systems for generating EUV light have been known in general, which include an LPP (Laser Produced Plasma) type system in which plasma generated by irradiating a target material with a laser beam is used, a DPP (Discharge Produced Plasma) type system in which plasma generated by electric discharge is used, and an SR (synchrotron radiation) type system in which orbital radiation is used.